1. Field of the Invention
The present invention relates to the field of nonvolatile memory devices. More specifically, the present invention relates to a multi-time programmable (MTP) memory and the fabrication methods for making the same.
2. Description of the Prior Art
Semiconductor memory devices have become more popular for use in various electronic devices. For example, non-volatile memory (NVM) is widely used in cellular telephones, digital cameras, personal digital assistants, mobile computing devices, and other applications.
Generally, NVM may be divided into multi-time programmable (MTP) memory and one-time programmable (OTP) memory. MTP memory is multi-readable and multi-writable. For example, EEPROM and flash memory are designedly equipped with some corresponding electric circuits to support different operations such as programming, erasing and reading. OTP functions perfectly with electric circuits with mere programming and reading functions. Electric circuits for erasing operation are not required in OTP.
Single-poly NVM designs have been proposed which reduce the additional processing cost. A single-poly NVM forms the charge-storage floating gate with a single layer of polysilicon. Because the single-poly NVM is compatible with regular CMOS process, it is applied in the field of embedded memory, embedded nonvolatile memory in the mixed-mode circuits and micro-controllers (such as System on Chip, SOC).
It is known that programming of memory cell can be accomplished by hot electron injection techniques (also known as channel hot electron or CHE programming) and may be erased by FN tunneling via an erase gate. The prior art MTP memory has reduced erase efficiency because of parasitic capacitance.